1. Field of the Invention
The present invention relates to a method for managing defects which arise in an information recording medium, more particularly, to a method for creating/writing defect management information for an information recording medium, and to an apparatus and an optical disc using the method.
2. Description of the Related Art
Optical discs have come into wide use since the advent of CD (compact disc) and the demand for optical discs is expected to grow steadily with popularization of DVD (digital versatile disc). Optical discs include read-only discs such as CD-ROM and DVD-ROM, write-once discs such as CD-R and DVD-R, and rewritable discs such as CD-RW and DVD-RAM. Standard formats of CD-RW and DVD-RAM have released and standardization for VDR (video disc recorder) is in progress.
For rewritable optical discs such as DVD-RAM, defects which arise in their recording surface should be managed to achieve high reliable write/reproduction operation in a manner that data is not written to sectors in which read-out errors are detected beyond a predetermined level (hereinafter referred to as “defective” or “bad” sectors). To accomplish this, defect management is performed such that addresses of defective sectors are stored in a defect management table on the optical disc and data access to the defective sectors, write or read-out, is prohibited.
As shown in FIG. 1, the rewritable physical area of DVD-RAM has a lead-in area, a data area, and a lead-out area. The data area is divided into contiguous 24 groups, and guard area is situated before and behind each group. Each group is made up of a user area for recording data and a spare area which provides a storage area in place of defective portion of the user area.
The data area is also made up of a plurality of blocks, each of which consists of 16 sectors. The position of each sector is specified by a physical address which is given uniquely to each sector. When data is recorded, LSN (logical sector number) is assigned sequentially to every sector except defective ones.
Defect management information, or physical addresses of defective sectors within the data area are stored in DMA (defective management area), which is provided in four places, two in lead-in area and the other two in lead-out area, as shown in FIG. 1, to protect against the defects which may arise in the four DMA themselves.
The DMA is made up of two ECC (error correction code) blocks, or 32 sectors. The first ECC block consists of one sector for DDS (disc definition structure) and 15 other sectors for PDL (primary defect list). Sixteen sectors of the second ECC block are used for SDL (secondary defect list).
The examples of DDS, PDL, and SDL are illustrated in tables 1, 2, and 3, respectively.
TABLE 1DDS structureSizelocation(in byte)contents0~12DDS identifier (0A0Ah)21Reserved (00h)31Disc Certification flag4~74DDS/PDL8~92The number of groups 10~20472038Reserved (00h)
TABLE 2PDL structureSizelocation(in byte)contents0~12PDL identifier (0001h)2~32The number of entries in PDL4~74The 1st bad sector address 8~114The 2nd bad sector address.........
TABLE 3SDL structureSizelocation(in byte)Contents0~12SDL identifier (0002h)2~32Reserved (00h)4~74SDL update counter 8~158Spare area full flags16~216Reserved (00h)22~232The number of entries in SDL24~318The 1st bad sector address & the1st replacement sector address.........
Methods for creating and managing defect management information such as PDL and SDL are explained below with reference to DVD-RAM.
PDL Creation and Management (in Write Operation)
The optical disc, or DVD-RAM is tested by the manufacturer to determine the validity of each sector. To do this, data is written to each sector and then read out from that sector to check whether that sector is bad or not. Sectors in which read-out errors are detected beyond a predetermined level are classified as defective ones at the manufacturing time and their physical addresses are stored in the PDL one after another, as shown in FIG. 1.
If a user requests to write data to the optical disc, a write command is sent to the optical disc drive and then the data begins to be written to unused sectors on the user area sequentially, as shown in FIG. 2. Each time data is written to the target sector, the physical address of the target sector is compared to those of defective sectors in the PDL. If the target sector is matched with one of defective sectors in the PDL, the target sector is skipped and the data is written to the next valid sector. This scheme to compensate for defective sectors is called “slipping replacement”.
In case where there is no defective sector on the user area, data is written only on the user area, as shown in the upper layout of FIG. 2. On the other hand, if there are defective sectors in the PDL, as many sectors in the spare area as defective sectors in the user area are used for sector replacement, as shown in the lower layout of FIG. 2.
A sector may become defective due to a deterioration in quality by cyclic reproduction operation of the optical disc. Such a defective sector is referred to as a “grown” defective one. Hence, when data is written to the optical disc, every sector which has not been listed in the PDL is examined to determine if it has a grown defect. Each sector identified as defective one is subjected to the sector slipping algorithm and the address of that sector is added to the PDL to guarantee that data is not written to the defective sector without sector verification process from the next write operation on.
In this way, the number of entries in the PDL increases as the write operation is repeated.
The criterion by which a sector is identified as bad one is as follows. A sector with ECC (hereinafter referred to as “ECC sector”) is constructed by data of 182 bytes×13 rows, as shown in FIG. 5, and a PID (physical identification) is assigned uniquely to each sector. The PID is written on each sector at four reserved locations. The sector is determined as defective sector if there are three or more errors in the PID read-out in one sector or if the number of rows having four or more error bytes in one sector is one or more. ECC block is classified as bad one when the number of rows having four or more error bytes in one ECC block is six or more.
SDL Creation and Management (in Reproduction Operation)
When the optical disc is placed into service, sectors on the disc may become defective. Hence, while reproducing the optical disc, sectors which have not been listed in the PDL are examined to determine whether or not they became grown defective sectors. If one sector is determined as bad one, data recorded in 16 logical sectors of the ECC block having the bad sector (bad ECC block) is transferred to a valid ECC block which is available on the spare area sequentially, as shown in FIG. 3. This scheme is called “linear replacement”. Then, a pair of the physical address of the first or head sector of the defective ECC block and the physical address of the first sector of the replacement ECC block is stored as an entry of the SDL.
When there is a lack of usable spare blocks in a present group, full flag corresponding to the group in the SDL is set to 1 and valid spare blocks are borrowed for linear replacement from the spare area of another group.
In reproduction operation, each ECC block is determined as bad one if the number of rows having four or more error bytes in one ECC block is eight or more or if there are one or more sectors in which more than three PID read-out arise.
When data is written to or read out from a DVD-RAM, a logical block address which is sent from the associated host computer to a DVD-RAM drive is translated to a physical target address. The PDL is then reviewed to determine if any slip adjustment is needed. That is, the physical target address is compared to those of defective sectors in the PDL. If it is determined that the sector at the physical target address is defective, the defective sector is skipped and the subsequent sectors are examined until a valid sector is found. Then the physical target address is adjusted so as to locate the next valid rector. In reproduction operation, the physical target address is compared to the list of the SDL to check if any sector replacement is required. If the physical target address is matched with one of those in the SDL, the physical target address of the replacement sector is read out from the SDL.
In case of optical disc which is dedicated to moving pictures or speech, it is crucial that the audio/video data is reproduced in real-time. However, the reproduction operation is interrupted for a short period of time corresponding to the sector replacement requiring data movement on the optical disc when grown defective sectors which have not been listed in the SDL are detected during reproduction. In this case, the reproduction speed of data recorded on the defective sectors is lowered, resulting in a short interruption of reproduction of audio/video data.
No management of new defective areas which have not been listed in the PDL and SDL at the reproduction time can be a method for solving the short interruption by the linear replacement. In this case, however, when the already-written audio/video data is erased and then a new audio/video data is overwritten to the VDR, the new data may be written to the defective sectors or blocks. As a result, read-out error of audio/video data which is newly recorded on such defective sectors or books cannot be avoid.